Amnesty said it was "deeply dismayed" that China and Russia are continuing to send arms "that are diverted for the conflict in Darfur and used there and across the border in Chad to commit grave violations of international law."
Along with Britain, France and the United States, China and Russia are permanent members of the UN Security Council, which adopted an extensive arms embargo in 2005.
Amnesty said that Russian and Chinese state-owned arms firms had supplied Sudan's government with a range of arms and ammunition, ranging from aircraft to light weapons.
The governments of Russia and China have denied Amnesty's accusations.
In Moscow, a foreign ministry spokesman rejected the report, saying: "None of our arms are being supplied to Darfur."
"We rigorously observe the provisions of the UN resolution banning deliveries of arms to Darfur," he said.
In Beijing, Jiang Yu, a foreign ministry spokeswoman, called the report "a groundless accusation".
"The Chinese government takes a responsible attitude and a strict management policy on arms exports," she said.
Amnesty International's 24-page report contained several photographs of Russian and Chinese warplanes which it said were based at Nyala airport in the Darfur region in the last few months.
The report also said that Sudan imported $24m worth of arms and ammunition from China, in addition to nearly $57m worth of parts and aircraft equipment and $2m dollars worth of parts of helicopters and airplanes.
It added that the Chinese company AviChina Industry and Technology "recently delivered six K-8 military training/attack aircraft to the Sudanese Air Force and a further six will follow soon."
Civilians in Darfur have often described coming under aerial attack from the Sudanese air force.